RL321

Hi, I am planning to move to U.K. and start earning income in UK from Jan 2025. My husband already in UK in 2024, he rented an apartment and included me as one of the tenant. I will visit him in Sept for 23 days. Then I go back to my home country. I still have my job and rented apartment in overseas before I go to U.K. in Jan 2025. Hence, I can apply split year, but when will be the date I need to declare income for tax purposes? Is it the date I visit UK in Sept, the date the tenancy agreement start in Aug or the date I start my job in U.K.? Thanks.